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Subject[PATCH 5.0 138/238] ext2: Fix underflow in ext2_max_size()
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5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit 1c2d14212b15a60300a2d4f6364753e87394c521 upstream.

When ext2 filesystem is created with 64k block size, ext2_max_size()
will return value less than 0. Also, we cannot write any file in this fs
since the sb->maxbytes is less than 0. The core of the problem is that
the size of block index tree for such large block size is more than
i_blocks can carry. So fix the computation to count with this
possibility.

File size limits computed with the new function for the full range of
possible block sizes look like:

bits file_size
10 17247252480
11 275415851008
12 2196873666560
13 2197948973056
14 2198486220800
15 2198754754560
16 2198888906752

CC: stable@vger.kernel.org
Reported-by: yangerkun <yangerkun@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext2/super.c | 41 ++++++++++++++++++++++++++---------------
1 file changed, 26 insertions(+), 15 deletions(-)

--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -757,7 +757,8 @@ static loff_t ext2_max_size(int bits)
{
loff_t res = EXT2_NDIR_BLOCKS;
int meta_blocks;
- loff_t upper_limit;
+ unsigned int upper_limit;
+ unsigned int ppb = 1 << (bits-2);

/* This is calculated to be the largest file size for a
* dense, file such that the total number of
@@ -771,24 +772,34 @@ static loff_t ext2_max_size(int bits)
/* total blocks in file system block size */
upper_limit >>= (bits - 9);

-
- /* indirect blocks */
- meta_blocks = 1;
- /* double indirect blocks */
- meta_blocks += 1 + (1LL << (bits-2));
- /* tripple indirect blocks */
- meta_blocks += 1 + (1LL << (bits-2)) + (1LL << (2*(bits-2)));
-
- upper_limit -= meta_blocks;
- upper_limit <<= bits;
-
+ /* Compute how many blocks we can address by block tree */
res += 1LL << (bits-2);
res += 1LL << (2*(bits-2));
res += 1LL << (3*(bits-2));
+ /* Does block tree limit file size? */
+ if (res < upper_limit)
+ goto check_lfs;
+
+ res = upper_limit;
+ /* How many metadata blocks are needed for addressing upper_limit? */
+ upper_limit -= EXT2_NDIR_BLOCKS;
+ /* indirect blocks */
+ meta_blocks = 1;
+ upper_limit -= ppb;
+ /* double indirect blocks */
+ if (upper_limit < ppb * ppb) {
+ meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb);
+ res -= meta_blocks;
+ goto check_lfs;
+ }
+ meta_blocks += 1 + ppb;
+ upper_limit -= ppb * ppb;
+ /* tripple indirect blocks for the rest */
+ meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb) +
+ DIV_ROUND_UP(upper_limit, ppb*ppb);
+ res -= meta_blocks;
+check_lfs:
res <<= bits;
- if (res > upper_limit)
- res = upper_limit;
-
if (res > MAX_LFS_FILESIZE)
res = MAX_LFS_FILESIZE;


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